1. Field of the Invention
The present invention relates to a rotary electronic component having another component placed inside it.
2. Background Art
As a conventional rotary electronic component, a rotary variable resistor will be described as follows with reference to FIGS. 5 to 7. FIG. 5 is a cross sectional view of the rotary variable resistor as the conventional rotary electronic component, FIG. 6 is an exploded perspective view of the rotary electronic component, and FIG. 7 is a cross sectional view showing a mounted state of the rotary electronic component.
In FIGS. 5 and 6, rotary variable resistor 10 includes case 1 made of an insulating resin. Case 1 is approximately annular having hollow portion 1A at its center. The annular portion of case 1 forms an open-top recessed portion, and hollow portion 1A is formed by a cylindrical wall protruding upward, which is cylindrical portion 1B. The recessed portion of case 1 has approximately annular resistor 2 placed on its bottom. Resistor 2 placed inside the recessed portion of case 1 is provided on its upper surface with a predetermined resistance part and a conductive part (neither is illustrated). The resistance part and conductive part have terminals 4 at their ends for being connected with an external electric circuit. Ends of terminals 4 are led outside case 1.
Rotary variable resistor 10 further includes operation body 3 made of an insulating resin. Operation body 3 has cylindrical operation portion 3A and flange 3B formed at the bottom end of operation portion 3A. Case 1 and operation body 3 are combined with each other in such a manner that the inner surface of operation portion 3A is set outside the outer surface of cylindrical portion 1B so that cylindrical portion 1B and operation portion 3A can rotate relative to each other. The bottom surface of flange 3B of operation body 3 has brush 5 fixed thereto, which is made of elastic metal. The tip of brush 5 is in slidable contact with the resistance part and conductive part of resistor 2. Rotary variable resistor 10 further includes cover 6 made of a thin metal plate. Cover 6 has an approximately ring shape to conform to the approximate annular shape of case 1. Cover 6 is provided over the recessed portion of case 1 to keep resistor 2 and flange 3B of operation body 3 inside the recessed portion. In this condition, cylindrical portion 1B of case 1 and operation portion 3A of operation body 3 protrude upward from circular central hole 6A of cover 6.
In rotary variable resistor 10 thus structured as a conventional rotary electronic component, rotating operation portion 3A of operation body 3 makes operation body 3 rotate relative to cylindrical portion 1B of case 1. This rotation allows brush 5 on the bottom surface of flange 3B to slide in elastic contact with the resistance part and conductive part of resistor 2. As a result, a resistance value corresponding to the rotated position is obtained from terminals 4. As a typical mounted state, rotary variable resistor 10 is mounted on the wiring board of an electronic device (not illustrated) to be used, and another component is mounted in hollow portion 1A.
For example, as shown in FIG. 7, when rotary encoder 11 is combined as another component, rotary encoder 11 is positioned on wiring board 7 inside hollow portion 1A in such a manner that rotary variable resistor 10 is coaxial with the axis of the rotation of rotary encoder 11. Rotary encoder 11 includes terminal 13 which is led outside from main body 12 of rotary encoder 11 and is soldered to wiring board 7. Rotary encoder 11 also includes cylindrical bearing 14 disposed above approximately rectangular main body 12 to rotatably support operating shaft 15 protruding upward. The rotation of operating shaft 15 enables a functional component formed inside main body 12 to provide a predetermined pulse signal through terminal 13.
Operation portion 3A of operation body 3 of rotary variable resistor 10 is fitted with approximately annular outside knob 16 having a circular recess in its upper portion. On the other hand, operating shaft 15 of rotary encoder 11 is fitted with inside knob 17 having a flat circular shape in such a manner as to be positioned in the circular recess of outside knob 16. As described above, most of the conventional rotary electronic components have a coaxial double operating knob structure in which rotary variable resistor 10 is rotated by turning outside knob 16, and rotary encoder 11 is rotated by turning inside knob 17. This structure is disclosed, for example, in Japanese Patent Unexamined Publication No. 2000-195375.
However, rotary variable resistor 10, which is one of the conventional rotary electronic components, has the following disadvantage. As shown in FIG. 7, when rotary encoder 11 as another component is placed inside hollow portion LA, and outside knob 16 and inside knob 17 are fitted respectively to rotary variable resistor 10 and rotary encoder 11 to rotate them, their rotation axes are difficult to align with each other, and are sometimes misaligned.
To overcome this disadvantage, when the coaxial double operating knobs, that is, outside knob 16 and inside knob 17 are used, it is necessary to absorb the misalignment by providing a large clearance between outside knob 16 and inside knob 17. This may decrease the quality of the electronic device on which rotary variable resistor 10 with rotary encoder 11 is mounted.